Red blood cells (erythrocytes - from Greek erythros for ‘red’ and kytos for ‘hollow’, with cyte translated as ‘cell’ in modern terms) are made in the bone marrow in a process called haematopoiesis where they lose their nucleus, as a child all bones produce blood cells but, as you age some bones start to stop producing them.
Bone marrow that produces them is called red bone marrow and the marrow that doesn’t, yellow bone marrow. They are the most common of the blood cells of which there are 5-6 litres of per adult. The primary function of the red blood cell is to carry oxygen around the body (it carries 97%, the other 3% is carried by dissolving oxygen in the plasma) and to remove waste via the circulatory system; e.g. carbon dioxide, as a waste product of respiration. It has special features that allow it to do these tasks with more efficiency - the haemoglobin (with iron as an important component) in the cell allows it to carry oxygen, as the oxygen latches onto the haemoglobin. This makes the cell somewhere between 30 to 100 times more efficient than plasma at carrying and transporting oxygen.
Red blood cells are traditionally seen as red but it is not the cell which is red, the oxygenated haemoglobin gives it the actual redness; this turns a bluish colour when de-oxygenated. Red blood cells do not last long, only around 100 to 120 days, as they soon get worn out and die. This short life span causes the body to re-produce the cells very quickly, it is estimated that 2.4 million are produced every second. Another specialised feature of the cell is that it has a dimple in the middle to increase surface area, therefore allowing it to hold more oxygen. There are two factors that control red blood cell production; they are low oxygen levels and a hormone called erythropoietin.
Red blood cells were discovered by Jan Swammerdam when he was studying a frog’s blood in 1658 with a powerful microscope. In 1901 Karl Landsteiner discovered that there was more than one type of blood group. He called the three different types he found (A, B and C which was later renamed as O). The next year, 1902, a fourth and final group was discovered – AB by two of Landsteiner’s colleagues. In 1959, x-ray crystallography discovered the final secret of the red blood cell, the structure of its main protein – haemoglobin.